Since there is no known treatment cure, immune system function and its response to the infection have a crucial impact on the Ebola survival rate. Facts from prior research and pertaining to the current outbreak might be the basis of some valuable insight. If so, the key factors which affect the survival rate are a robust antibody response and a balance in the humoral and cell-mediated immune responses.
Back in the 1990s a team of French scientists conducted a study on 11 patients infected with the Ebola virus in Gabon and Congo West Africa. They analyzed the blood of the victims and compared the test results between the four that survived the infection and the seven that did not. They discovered some interesting differences. The blood of the survivors showed they had produced generous amounts of antibodies against the virus and had mounted a good cellular response to it. That response included a substantial number of cytotoxic lymphocytes and a modest amount of interferon. In contrast, the blood samples of the majority of the victims who did not survive the infection did not show the balance in the humoral and cellular responses. Instead, they showed sparse antibody production, an excess of lymphocytes and excessive amounts of interferon.
The imbalance in the two arms of defense is not surprising in that the theme of negative feedback loops is a recurrent one throughout the body and its various systems. The exaggerated cellular response most likely is an attempt to compensate for a relative deficiency of antibodies and/or an overload of virus. At any rate, it appears at that point the proverbial horse is out of the barn in terms of survival.
The impact of antibodies on the Ebola survival rate also seems apparent early on during this current outbreak, as was also the case during previous ones in Africa where recipients of convalescent serum survived the infection. Even though both groups acquired passive immunity from antibodies in that serum, it was the equivalent of their own immune systems producing the antibodies. The numbers are small in the French study and among the recent survivors treated with the serum of prior survivors, but the facts are encouraging for an infection with such a low survival rate.
In spite of the importance of humoral immunity in combating Ebola the cellular response is also very important. One reason is because antibodies are not reusable and don’t have an indefinite shelf life in the body. B cell activation and the subsequent events involving cell-mediated immunity must occur in order for a continuous and adequate supply of antibodies to be available to combat an ongoing infection. Even though, as far as we know to date, the Ebola virus does not infest lymphocytes, its infestation of other antigen presenting cells can interfere with their normal function. The end result is direct disruption of cell-mediated immune system function and an indirect blunting of the humoral immune response. Moreover, memory cells are required for future resistance to the virus.
Despite it being such a lethal disease, the pathogenesis of Ebola is not entirely clear. Like other viruses though, Ebola requires a host cell in order to replicate or multiply. A host is an organism that enables another one to survive and carry out its functions. Unfortunately, in the case of Ebola, humans are a host. The virus can replicate in various cells of the body where it wreaks havoc. The immune system cells in which it multiplies are dendritic cells, macrophages, and monocytes. Because of the important role these cells play in immunity against viruses, it is understandable that the invasion and disablement of them by the Ebola virus has a negative impact on survival.
Antibodies defend against viruses by neutralizing them or causing them to lose their infectivity. They can do so by interfering with viruses binding to the receptors of cells, their entry into cells, or their release of their set of genes inside of cells. In some instances they cause viruses to cluster together or destroy them by lysing their membranes. The net effect is the prevention of viral replication. Hence, the early production of antibodies against Ebola is an important means of limiting its proliferation and ridding the body of it.
The impact of antibody response on the Ebola survival rate might be even greater than it appears. In some cases Ebola exposure might cause such a robust antibody response that it leads to clearing of the virus and resistance to it without typical symptoms developing. This phenomenon – acquired immunity – might also explain why some natives of Ebola-stricken villages and health workers have been stricken with the illness and others haven’t.
There is a need for much research on what impacts the Ebola survival rate. The good news and the bad news is there has not been the number of cases or survivors in parts of the world to conduct reliable research. The good news and the bad news is also that appears to be changing.
Heretofore, testing has focused mainly on detecting the antigen in order to make a diagnosis. Research based on antibody testing might provide some important clues though. Random antibody testing of natives who live in Ebola stricken villages might be a worthwhile research pursuit. Another meaningful research study might be the serial measurement of antibodies on patients recovering from Ebola. Such research might show if there is a correlation between the quantity of antibodies produced and the survival rate. It might also show if there is a relationship between a rise in quantity of antibodies and the speed of recovery.